The combination of biotransformations and metal-assisted catalysis within hybrid systems represents a promising strategy to extend the repertoire of reactions enabled in a biomolecular environment. Both covalent catalytic entities and supramolecular assemblies have been created recently to mediate transformations otherwise difficult to perform in 'classical' biocatalysis. In this context, various biopolymers can serve as ligand spheres simultaneously acting as chiral inducers. In particular, modular approaches embedding novel metal-based catalytic centers via an affinity interaction are highly appealing, as this technology may serve as a versatile platform to incorporate diverse reactivities in a biological matrix in a stereoselective fashion. (c) 2007 Society of Chemical Industry.